Usually, my blood sugar level is around 100 mg/dL. Lately I started to fast, 24 or 48 hours. After I fast, say for 48 hours, my glycemia is around 80 mg/dL. Today I measured my glycemia before broking an 80 hours fast, and, boom, 118 mg/dL! What gives? In the last 3 days I just drank water and black coffee, zero food. Where did all that sugar come from?
edited: I measured the blood sugar level on an empty stomach.
I’m a type 1 diabetic and enjoy doing fasts!
Because I have a glucose monitor I can see what my blood glucose does throughout a fast. For me, its not uncommon that I have a high bg during the first two days of a fast (which would be extremely high for you), due to the glycogen storage in my liver.
Depending on activity level, it may take longer for you to get through all of your glucose storage
The caffeine in coffee can also cause a slight glucose spike (in me at least)
Muscles also store glucose, so even after your liver is depleted, your muscles can cause a spike!
From WP:
Gluconeogenesis is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates. It is a ubiquitous process, present in plants, animals, fungi, bacteria, and other microorganisms. And humans.
Your liver is capable of producing glucose as the demands from your body dictate. (see references to “Dawn Phenomenon”)
This is why there are no ‘essential’ carbohydrates, by the way.
I forget the exact pathway but I think cortisol stimulates glycogen decomposition in the liver. I know diabetics usually have higher blood sugar in the morning because of this. Levels should peak around 8 am based on your location/exposure to natural light. Take it again around noon, you should be low again.